1. Field Of The Invention
This invention relates to the preparation of poly-(alkylpentamethyleneterephthalamide), especially poly-(2-methylpentamethyleneterephthalamide), into which there can be incorporated by condensation up to 50 mole percent, with respect to the sum of all dicarboxylic acid or diamine moieties, of other diamines, dicarboxylic acids and/or aminocarboxylic acids or their lactams. More especially this invention contemplates a process for the preparation of such poly-(alkylpentamethyleneterephthalamides) wherein a pre-product is formed by heating an aqueous solution of the corresponding nylon salt and a still water soluble oligomide from a temperature of below 150.degree.C. up to a polycondensation temperature of at least 250.degree.C. The process is conducted preferably while maintaining the nylon salt/oligomide mixture at a stirrable consistency while the same is heated up to a polycondensation temperature.
2. Discussion Of The Prior Art
Polyamides into which moieties of terephthalic acid and of 2-methylpentamethylenediamine, among others, are incorporated by condensation are already known. They are difficult to prepare by the melt condensation methods of the prior art. The reason for this is that the special diamine is easily cyclized to methylpiperidine, whereupon--as long as free diamine is present in the reaction mixture--ammonia is liberated. To the extent that one of the two amino groups of this diamine has already entered a carbonamide bond, a CONH.sub.2 terminal group remains as a result of the formation of methyl piperidine, and acts to break the chain. The conventional melt condensation process as used, say, for the preparation of nylon 66, accordingly lead to high diamine losses which are not easy to compensate since the magnitude of these losses is not consistent.
Therefore, a method has already been proposed for the preparation of poly-(2-methylpentamethyleneterephthalamide) which consists in heating in a closed autoclave a mixture of terephthalic acid and 2-methylpentamethylenediamine with the amount of water necessary to dissolve the nylon salt formed from these substances, to bring it to temperatures that will permit the formation of amide groups. From this reaction mixture the oligoamides that form are isolated and refined and then condensed at still higher temperature with the removal of the equilibrium water present and of the newly formed reaction water (Japanese Pat. No. 19 551/69). It is well known that this process is not economical both on account of the complexity of the process and on account of the relatively low yields.
Accordingly, it has become desirable to provide a method for the preparation of poly-(alkylpentamethyleneterephthalamides) whereby the undesired secondary reactions mentioned supra can be minimized. Moreover, it has become desirable to provide such a process whereby the poly-(alkylpentamethyleneterephthalamides) are prepared such that they have a relative viscosity of at least 1.8 and preferably above 2.0.